It is on a 2005 Craftsman lawn tractor. It will only run on the left side. Had the carb rebuilt, no help. Has 160 lbs comp in both cylinders. Took valve covers off and watched movment, looks fine. Checked clearance, .012 on both the int. and exh. on both cylinders. Has spark on both sides. switched coils anyway from side to side, no change. Plug is wet with gas on dead side.

Thanks for the responce. I will readjust the valves, as that is an issue, but I doubt that is my main issue.

I do have both spark and gas on both cylinders. I have switch the magneto coils from side to side and the dead cylinder stays the same. I understand that this makes no sense, but it is fact. The ignition timing can not change as you can not move the magnetos side ways, only in and out and I set them to about .005 from the fly wheel

You'll need to do more forensic testing..the plug might be junk,the coil might have "good spark" in open air and not when under compression in the cylinder (though I see your point it dont make sense after swapping them side to side)..if its a magneto type coil that does not use 12V power to make the spark,maybe the magnet in the flywheel is getting weak ..I'd try the cheapest thing first,brand new spark plugs..(not Champions if it were mine!)..

Maybe the spark plug is only sparking intermittently. I had a Command series OHV engine that would not run at all, just backfire. I checked the valve clearance and the flywheel for a sheared key and those were just fine, but found the almost brand new spark plug to be the culprit.

Hi guys, I'm a newbie so please bear with me. My rider-tractor has 21 hp B&S Intek engine. I tried starting it the other day and kept running the starter until the battery died and it was firing up, no smoke, nothing but dry cranking. I charged the battery and now it won't even crank. When I turn the key, I hear a loud click from the ammeter (battery meter on the dash) as the needle dives all the way down to negative. I swapped out the starter with another engine but that didn't change anything. Do you think it's the voltage regulator? I checked the 30 amp fuse and it's not that either. Thanks for a great forum! Any advice would be really appreciated.

Well I would disconnect the Kill Wire from the base of BOTH coils and see what happens. By the way, weak flywheel magnet is not going to affect one coil and not the other one. I think you are overlooking something, I'd suggest you retrace your test procedure.

Thanks, Walt. I'm embarrassed to say I don't know what a kill wire is nor where to locate it. I did run a jumper cable from the battery to the starter this morning and it cranked the motor but it didn't start. That takes the starter out of the diagnosis. Is there a solenoid or something between the starter and the battery? The way I see it, but I'm probably wrong, the problem is somewhere in-between the battery and the starter motor. Thanks!!

Thanks, Brad and Truckintyler. Right now the weather is closing in fast and I won't be able to do anything for a day or two but I'm making a checklist and the solenoid and coil are on the list. Incidentally, is there some way of testing either with a standard voltage-ohms-amp meter? In other words, how would I know one of them is defective? I don't really have anything on the shelf to swap out. Thanks!

Solenoid either works or it doesn't, coil I'm pretty sure the manual says it can't be checked for resistance ,
I had a briggs single that really ticked me off, it was trying to run and backfiring, I changed the coil spark plug changed the carb for a known good one, changed the headgasket and clyinder head ( I have alot of parts as I flip lawn tractors)
Anyways it ended up being a sheared flywheel key which made me feel like an idiot.

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